298 CLASS VIII. 
Sub-genera Petrobius, Machilis Lracu. 
Sp. Machilis maritima Latr., M. polypoda DuMER. (not Latr.), Cons. gén. 
Pl. 54, fig. 2, &e. Besides the jointed threads (two on most of the seg- 
ments of the abdomen), Gu&RIN has observed in Machilis vesicles also on 
the same segments, which he compares to gills; Ann. des Sc. nat. sec. 
Série, Zool. v. pp. 374, 375, Iconogr., Ins. Pl. 1. fig. 1 f. These animals 
remind us of larvae of Hphemera. 
Lepisma L, (in part). Antenne inserted amongst eyes, small, 
remote. Palps moderate. Body depressed, squamose, not saltatory, 
terminated by three subequal sete. 
Sp. Lepisma saccharina L., Guirin Iconogr., Ins. Pl. 2, fig. 2; GEOFFROY 
Ins. Par. 1. Pl. xx. fig. 3; Hooxs Micrographia 1667, Tab. 33, f. 3, 
pp. 208—210. Itis said that this insect was imported into Europe from 
America, where it lives in sugar: in Sweden it is rare, according to Dr 
GEER ; it is not spotted, covered with silvery scales, which under the 
microscope are finely ribbed longitudinally, and differ much in size and 
form. This insect runs very rapidly, and with us is usually found in 
clothes-chests, between damp books, &c. 
Sub-genus Lepismina GERY. is distinguished by the body plane, 
the thorax very broad. 
Sp. Lepisma aurea Léon Durour, Ann. des Se. nat. Tom. Xxu. p. 419. Tab. 
I Io, Me 
Jote—Genus Vicoletia GERVAIS is distinguished by defect of 
eyes, and body not scaly ; Campodea Wxstwoop, Ann. of Nat. Hist. 
Tom. x. 1842, p. 71, by the same characters and by the tail com- 
posed of two sete only. Is it Podwra ambulans L. } 
Family IV. Podurelle. Body in some elongate, in others globose, 
broad, covered usually with hairs, sometimes with scales also. 
Antenne with few joints, or with four longer joints at the base, at 
the apex only with short numerous joints. Palps inconspicuous. 
Abdomen composed of only six or fewer segments, mostly termi- 
nated by a forked tail, durmg rest bent forward beneath the 
abdomen, serving for springing. 
Podura L. 
Spring-tail (properly foot-tail, since the tail is used like feet for 
motion). They are small insects, which live on trees, under bark, 
under stones, on moist earth, &e. Some are met with on the surface 
of water. Since the tail, according to Waaa, is at first wanting 
in young animals (Ann. de la Soc. Entom. de France, x1. quoted by 
